java - How to disable a button from another activity -

i have little login program saves data shared preferences. main activity has "login" , "account" buttons. want disable login button when shared preferences null , enable "account" button user sign account second activity. how can enable/disable 2 buttons if shared preferences null?

1. activity 1

   protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.main_interface);  final button login = (button)findviewbyid(r.id.login); final button account = (button)findviewbyid(r.id.account); login.setenabled(false); login.setonclicklistener(new onclicklistener() {     public void onclick(view arg0) {         startactivity(new intent(mainactivity.this, summation.class));      } });   account.setonclicklistener(new onclicklistener() {     public void onclick(view arg0) {         startactivity(new intent(mainactivity.this, append.class));     } }); button exit = (button)findviewbyid(r.id.exit); exit.setonclicklistener(new onclicklistener() {     public void onclick(view arg0) {         finish();         system.exit(0);     } }); 

2. activity 2

    protected void oncreate(bundle savedinstancestate){  super.oncreate(savedinstancestate);  stetho.initializewithdefaults(this);  setcontentview(r.layout.append_interface);   final edittext usernameappend = (edittext)findviewbyid(r.id.usernameappend); final edittext passwordappend = (edittext)findviewbyid(r.id.passwordappend);  //this buttons appends username , password sharedpreferences button append = (button)findviewbyid(r.id.append); append.setonclicklistener(new view.onclicklistener() {      public void onclick(view arg0) {          final sharedpreferences mysharedpref = getsharedpreferences(pref_name, mode_private);          final sharedpreferences.editor editor = mysharedpref.edit();         //append data          final string un = usernameappend.gettext().tostring();          editor.putstring(editorusername,un);          editor.commit();          final string pw = passwordappend.gettext().tostring();          editor.putstring(editorpassword, pw);          editor.commit();         if(mysharedpref != null){             toast.maketext(append.this,"account saved",toast.length_long).show();              startactivity(new intent(append.this, mainactivity.class));          }else{             toast.maketext(append.this,"please enter again",toast.length_long).show();          }          }      } ); //exit button,, exits app button exit = (button)findviewbyid(r.id.exit); exit.setonclicklistener(new view.onclicklistener() { public void onclick(view arg0) {     finish();     system.exit(0);      }  });   } 

in 1st activity check either shared preference exists or not. first time null.

     btnlogin.setenabled(false);      btnaccount.setenabled(false);      sharedpreferences mprefs=this.getsharedpreferences(your_preference_name,context.mode_private);     if(mprefs==null)     {         btnaccount.setenabled(true);     }     btnaccount.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view view) {          }     });     btnlogin.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view view) {          }     });